1. Field of the Invention
The present invention relates to an information distribution system, a terminal apparatus used in the same system and a recording medium on which a program is recorded, as well as a loop connection avoidance method, and particularly to an information distribution system which distributes contents information in a network in which a plurality of terminal apparatus are mutually connected by forming the duplicated tree topology, a terminal apparatus used in the same system and a recording medium on which a program is recorded, as well as a loop connection avoidance method.
2. Description of the Related Art
To date, there is a technology called an ALM (Application Layer Multicast), which carries out a relay distribution of information on a contents stream (hereafter referred to as contents information), while managing a contents distribution route in an application layer. This technology is one which distributes the contents information by carrying out a P2P (Peer to Peer) communication between nodes (hereafter referred to as terminal apparatus) such as personal computers or STB (Set Top Box) apparatus.
In this kind of ALM technology, depending on differences in a distribution topology management method and construction method, they are divided into the following kinds of method. That is, depending on the differences in the distribution topology management method, they are divided into a hybrid type P2P and a pure type P2P method, while depending on the differences in the distribution topology construction method, they are divided into a Mesh-First approach, a Tree-First approach and an Implicit approach method.
The hybrid type P2P is a method in which a designated server apparatus manages common topology information, while the pure type P2P is a method in which individual terminal apparatus manage partial topology information. Also, the Mesh-First approach is a method in which terminal apparatus construct a mesh-shaped topology, and select a distribution route for distributing a data stream therefrom by means of an RPF (Reverse Path Forwarding) or the like, the Tree-First approach is a method in which terminal apparatus construct a tree-shaped topology, from which each terminal apparatus searches for an adjacent terminal apparatus, and renders redundant a spare distribution route, and the Implicit approach is a method in which terminal apparatus construct a control data topology using a specific metric, and make that itself a distribution route (a method of an approach by which a tree and a mesh are made simultaneously).
The mesh type topology, not being limited to a technology field of the heretofore described ALM, is also employed in a technology field of an IP multicast or a LAN. In the mesh type topology, as it is constructed of a tight control communication network in which a certain terminal apparatus has a connection relationship with a plurality of terminal apparatus, a duplicated topology is constructed in order to guarantee continual operations, even in a case in which a connection between terminal apparatus is cut off and a stream cut off event occurs.
However, in the event that the connection between the terminal apparatus is cut off, reconstructing the distribution route randomly will result in a loop connection occurring in a distribution route. Therein, as a method of avoiding this kind of distribution route loop connection, there is, for example, the one described in Japanese Unexamined Patent Publication No. 2000-49779. Although the method in the patent publication does not target duplicated mesh type topology, in the technology field of the ALM, which has a mesh type topology, a distribution route between a root terminal apparatus and a targeted terminal apparatus (a root path) is sought by sending a packet which stores route information along the distribution route, and a loop connection is detected by confirming that the targeted terminal apparatus is not included in the root path. Then, in an upstream selection process when an upstream terminal apparatus is reconnected, by selecting an upstream terminal apparatus having a root path which does not include the own terminal apparatus itself, the loop connection is avoided.
The heretofore described method of Japanese Unexamined Patent Publication No. 2000-49779, in the event of finding an upstream substitute node in order to avoid a distribution route loop, uses a protocol which transmits a search message in an upstream direction from a targeted terminal apparatus. For this reason, in the event that a plurality of terminal apparatus attempt to widen a search range and execute a process, there has been a problem in that search messages concentrate in an upstream terminal apparatus, and a processing load increases.